To be suitable for use as an ink-jet receiver, a material is preferably quick to absorb applied ink and also, once dry, printed images are preferably stable when subjected to light and ozone. Ink-jet media having a porous layer are typically formed of inorganic materials with a polymeric binder. When ink is applied to the medium it is absorbed quickly into the porous layer by capillary action. However, the open nature of the layer can contribute to a lack of stability of printed images when subjected to light and ozone. Ink-jet media having a non-porous layer are typically formed by the coating of one or more polymeric layers onto a support. When ink is applied to such media, the polymeric layers swell and absorb the applied ink. However, due to limitations of the swelling mechanism, this type of media is slow to absorb the ink, but once dry, printed images are often stable when subjected to light and ozone.
Polymer foams have been developed that are suitable for use as inkjet receivers. The materials, as disclosed for example in our co-pending European Patent Application Number 03015858.8, can be both quick to absorb applied ink and also provide images that are stable to light and ozone once dry.
Traditionally, polymer foams are manufactured using mostly hydrophobic thermoplastic materials such as polyurethane, PVC and polyethylene. Initially a gas filled polymer is created using a known foaming method, the gas-filled polymer then being coated onto a support substrate.
Typical-foaming methods include:
                1. Thermal decomposition of chemical blowing agents, generating N2 or CO2, by application of heat or as a result of the exothermic heat of reaction during polymerisation.        2. Mechanical whipping of gases into a polymer melt, which hardens either by catalytic action or heat, trapping gas bubbles in a matrix.        3. The use of low boiling point liquids which boil at low temperatures thereby creating gas.        4. Expansion of a gas dissolved in a polymer upon reduction of pressure in the system.        5. Incorporation of microspheres into a polymer mass, the microspheres consisting of gas filled polymer that expands upon heating.        
After obtaining the gas filled polymer by one or more of the methods above, the material is then formed, typically, using one of three common manufacturing processes:
1. Compression moulding
2. Reaction injection moulding or
3. Extrusion of the foam.
The temperatures involved in these processes can be very high, e.g. in excess of 150° C., as the polymers used are in their molten state. The most common processing method used in creating polymer foam films is extrusion. This is a three-stage operation consisting of forming a polymer solution with gas dissolved in it, by injection of N2 or CO2, or by the use of blowing agent, to create a single phase solution. Nucleation sites are then formed, as a result of a rapid pressure drop to create large numbers of uniform sites. Cell growth then takes place by means of diffusion of the gas to form bubbles. Control of the processing conditions provides the pressure and temperature changes necessary to control cell growth.
US-A-2001/0021726 (James F. Brown) discloses porous surface compositions and methods of retaining biological samples on the surface. The method relies on the use of curable polymers. U.S. Pat. No. 3,794,548 (C. Wirth et al) discloses the use of polyurethane as a porous polymer film. Polymer is heated causing volatilisation of solvents within the polymer resulting in a porous coating. U.S. Pat. No. 6,228,476 (Bogrett et al) relates to a foam insulation sheet made using curable polymers.